In the search for high performance materials, considerable interest has been focused upon pyrolyzed carbonaceous fibers. Graphite fibers are defined herein as fibers which consist essentially of carbon and have a predominant X-ray diffraction pattern characteristic of graphite. Amorphous carbon fibers or carbonized fibers, on the other hand, are defined as fibers in which the bulk of the fiber weight can be attributed to carbon and which exhibit an essentially amorphous X-ray diffraction pattern. Graphite fibers generally have a higher Young's modulus than do amorphous carbon fibers and, in addition, are more highly electrically and thermally conductive.
Industrial high performance materials of the future are projected to make substantial utilization of fiber reinforced composites, and pyrolyzed carbonaceous fibers theoretically have among the best properties of any fiber for use as high strength reinforcement. Among these desirable properties are corrosion and high temperature resistance, low density, high tensile strength, and high modulus. Graphite is one of the very few known materials whose tensile strength increases with temperature. A common technique employed in the production of composites involves the filament winding or molding of articles of the desired configuration utilizing continuous lengths of pyrolyzed carbonaceous filamentary materials having a coating of a resinous material which ultimately serves as the matrix in the resulting article. Uses for such fiber reinforced composites include aerospace structural components, rocket motor casings, deep-submergence vessels and ablative materials for heat shields on re-entry vehicles.
In the prior art organic fibrous materials such as pitch, cellulosics, acrylics, polyamides, polybenzimidazoles, polyvinyl alcohol, etc., have commonly served as the starting material in the production of pyrolyzed carbonaceous fibers. Such prior art conversion techniques commonly have employed a thermal stabilization step prior to carbonization or carbonization and graphitization. Such thermal stabilization step commonly has been conducted either by chemical means or by moderate heating for a sufficient time in an appropriate gaseous atmosphere (i.e., at about 200 to 400.degree. C.) as is well known to those skilled in the art. The stabilized fibrous material next has been carbonized by heating in an inert atmosphere at a more highly elevated temperature wherein elements present in the same other than carbon are substantially evolved.
Representative disclosures involving the utilization of a pitch precursor include U.S. Pat. Nos. 3,595,946; 3,629,379; 3,639,953; and 3,702,054.
Representative disclosures involving the utilization of a cellulosic precursor include U.S. Pat. Nos. 3,011,981; 3,107,152; 3,116,975; and 3,305,315.
Representative disclosures involving the utilization of an acrylic precursor include U.S. Pat. Nos. 3,508,874; 3,539,295; 3,650,668; and 3,656,883.
Representative disclosures involving the utilization of a polyamide precursor include U.S. Pat. No. 3,547,584, and Belgian Patent Nos. 719,961; 720,356; and 722,216.
Representative disclosures involving the utilization of a polybenzimidazole precursor include U.S. Pat. Nos. 3,449,077, and 3,528,774.
Representative disclosures involving the utilization of a polyvinyl alcohol precursor include U.S. Pat. Nos. 3,427,120, and 3,488,151.
Many of the precursor materials utilized in the prior art have contained a substantial proportion of elements other than carbon which must be evolved during the carbonization reaction. Such precursor materials are commonly expensive and yield a decreased amount of pyrolyzed carbonaceous product because of a high material loss through the evolution of non-carbon components. Starting materials such as pitch are recognized to be inexpensive and to possess an extremely high carbon content; however, such materials have been known to present severe processing constraints because of difficulties commonly encountered when handling the same. For instance, pitch filamentary materials are commonly of low strength and brittle in nature, and extremely prone to damage.
It is an object of the invention to provide an improved process for the formation of pyrolyzed carbonaceous filamentary materials.
It is an object of the invention to provide an improved process for the formation of a pyrolyzed carbonaceous filamentary material which utilizes a relatively inexpensive precursor material of a relatively high carbon content.
It is an object of the invention to provide an improved process for the formation of a pyrolyzed carbonaceous filamentary material which utilizes a precursor material which may be readily melt spun.
It is another object of the invention to provide an improved process for the formation of a pyrolyzed carbonaceous filamentary material wherein the evolution of non-carbon off-gases during the carbonization reaction is minimized.
It is another object of the invention to provide an improved process for the formation of a pyrolyzed carbonaceous filamentary material which is substantially free of voids.
It is a further object of the invention to provide an improved process for the formation of a pyrolyzed carbonaceous filamentary material wherein the filamentary material undergoing thermal conversion may be readily handled without harmful results.
These and other objects, as well as the scope, nature, and utilization of the process will be apparent from the following description and appended claims.